Button-type batteries are small thin energy cells that are commonly used in watches and other electronic devices requiring a thin profile. FIGS. 1 and 2 show a conventional button-type battery 20. Battery 20 includes an anode 22, a cathode 24, a porous separator 26 separating the anode and cathode, and an electrolyte 28 which facilitates ion conductivity between the anode and cathode.
These internal battery components are housed within a metal casing formed by a lower conductive can 30 and an upper conductive lid 32. Can 30 electrically contacts cathode 24 and thereby forms the positive battery terminal. Lid 32 electrically contacts anode 22 to form the negative battery terminal. The can and lid are crimped or pressed together to form a fluid-tight seal 34 which entirely encloses the anode, cathode, separator, and electrolyte. An insulating gasket 36 is provided within primary seal 34 between lid 32 and can 30 to electrically insulate the two housing members.
There is a need in button-type battery usage to make such energy cells thinner. Today, the thinnest commercially available button-type battery has a thickness of 1.2 mm (47.2 mils). It would be desirable to make a thinner battery, particularly one having a thickness of less than 1 mm (39.4 mils). A countering concern, however, is that the integrity of the fluid-tight seal cannot be compromised simply to achieve the goal of thinner batteries.
Accordingly, it is desirable to design a button-type battery with a very thin profile, yet without degrading the integrity of the fluid-tight seal.
There is an evolving market for button-type batteries in personal carrying cards which employ such batteries. For example, smart cards, battery-back RAMs (Random Access Memories), and some credit cards are being manufactured with integrated circuitry and memory components that require a power source. It is desirable to form such integrated circuit cards as thin as standard magnetic-stripe credit cards which are widely used today. Credit cards have a nominal thickness requirement of approximately 30 mils (0.762 mm). A thin button-type battery of less than 30 mils (0.762 mm) thickness would be ideal for use in such integrated circuit carrying cards. However, conventional button-type batteries are too thick, inflexible and their seals easily rupture when bent. Once the fluid-tight seal ruptures, the electrolyte leaks from the battery, rendering the battery inoperable.
It would therefore be desirable to design a thin button-type battery with a thickness of less than 30 mils (0.762 mm), yet having high integrity seals that could be flexed and bent without destroying operation of the battery or rupturing the seal.